the blockade of d1/d2-like dopamine receptors within the dentate gyrus of hippocampus decreased the reinstatement of morphine-extinguished conditioned place preference in rats

introduction: the hippocampus (hip), the primary brain structure related to learning and memory, receives sparse but comprehensive dopamine innervations and contains dopamine d1/d2-like receptors. it is demonstrated that dopamine receptors in dentate gyrus (dg) region of hip have a remarkable function in spatial reward processing. much less is known about the involvement of hip and its d1/d2 dopamine receptors in drug-seeking behaviors, more particularly, in the morphine extinguished conditioned place preference (cpp). methods: to find out the role of d1/d2-like receptors within the dg in morphine-seeking behaviors, forty adult male albino wistar rats weighing 220-280g were unilaterally implanted by a cannula into the dg. the cpp paradigm was done conditioning score and locomotors activity were recorded by ethovision software. all drugs/vehicles were microinjected one day after extinction (just before the cpp test) into the dg as reinstatement day. results: the results showed that intra-dg administration of different dose of sch23390 (0.25, 1 and 4μg/0.5μl saline), as a selective d1-like receptor antagonist and sulpiride (0.25, 1 and 4μg/0.5μl dmso), as a selective d2-like receptor antagonist dose-dependently attenuated the morphine-extinguished cpp reinstated by priming injection of morphine (1 mg/kg, sc). discussion: it can be concluded that d1/d2-like receptors within this region have an important role in morphine-seeking behaviors in extinguished rats.